Electrolysis of aqueous salt solutions

Abstract

An electrolysis process is disclosed in which catholyte is transferred serially from one cell, in a bank of a plurality of cells, to the cathode compartment of a succeeding cell in the bank. The transfer is accomplished by means of a gas-lift in which gas, present in the cathode compartment rises through a confined space, which is dimensioned such that the gas serves to lift the catholyte upward to a point where the gas and liquid separate and the liquid catholyte is allowed to fall freely to a collection point from which it is introduced into the cathode compartment of a succeeding cell.

We claim: 
     
       1. In a process for producing chlorine and sodium hydroxide wherein aqueous sodium chloride is electrolyzed in a bank of a plurality of electrolytic cells, each cell having a cathode compartment and an anode compartment separated by a cationic permeable membrane, the improvement which comprises: (a) transferring the catholyte serially from the cathode compartment of one or more preceding cells to the cathode compartment of at least one succeeding cell in the bank and providing electrical isolation between the cathode compartment by means of a gas-lift in which hydrogen produced in the cathode compartment rises through the sodium hydroxide catholyte solution in a confined space and lifts said catholyte solution to a disengaging point where the hydrogen is separated and the catholyte is allowed to fall freely through a confined void space to a predetermined point where it is collected and fed by gravity to the cathode compartment of a succeeding cell; and   (b) maintaining the electric current on the cathode in said preceding cells such that C d  K=D/H, wherein C d  is the current density, D is the depth of the cathode compartment, H is the height of the cathode compartment and K is a proportionality constant having a value between 0.01 and 2.0.   
     
     
       2. A process according to claim 1 wherein K has a value between 0.05 and 1.0. 
     
     
       3. The method according to claim 1 wherein the difference between the hydraulic head generated by the presence of hydrogen gas in the catholyte solution and the hydraulic head required to feed the succeeding cell by gravity is equal to the difference in height between the separation point and the collection point.